Typically roofs are assembled on site. Walls are assembled and the rafters and other structure are assembled to form a complete roof. This is also true for glazed roof systems.
Glazed roof systems are used to form various types of roofs. These can include Georgian-style, conservatory-style and lean-to roofs. Glazed roof systems include panels supported between adjacent rafters. The rafters are supported at their upper end by a variety of structures such as a hip beam, a ridge beam, a wall plate or the like. At the opposite end, the rafters are supported by an eaves beam. This is a metal beam that has a structure adapted to support the rafter and form a seal at the lower end of the panels. The glazing is designed to prevent air and water ingress.
These units are all typically constructed on site because the eaves beam must be attached to the wall header prior to the rafters. The rafters in turn are fastened to the eaves beam with the glazing panel fastened to the rafters and hip beam. This on site construction is problematic simply because it is very labor intensive requiring a great deal of time to ensure that everything is properly installed to prevent leakage. Even with relatively small roofs, such as bay window roofs, on site fabrication is required.